Re: [PATCH v8 23/44] fetch.c: change s_update_ref to use a ref transaction

(+cc: peff for STORE_REF_ERROR_DF_CONFLICT expertise)
Ronnie Sahlberg wrote:

[...]

+	transaction = ref_transaction_begin();
+	if (!transaction ||
+	    ref_transaction_update(transaction, ref->name, ref->new_sha1,
+				   ref->old_sha1, 0, check_old) ||
+	    ref_transaction_commit(transaction, msg, NULL)) {
+		ref_transaction_rollback(transaction);
 		return errno == ENOTDIR ? STORE_REF_ERROR_DF_CONFLICT :
 					  STORE_REF_ERROR_OTHER;
+	}

I'd rather not rely on errno here (see the previous patch for why).
Is there some other way to distinguish the case where a ref couldn't
be created because there was a prefix of that ref in the way?

For example, maybe ref_transaction_commit could return a different
negative integer in this case.

Thanks,
Jonathan